Combined jet fuel-gasoline production



United States Patent 3,193 4% (IOMMNED JET FUEL-dAS-QLHNE PRODUCTIONDonald B. Broughton, Chicago, iii, assignor to Universal Gil ProductsCompany, Des laines, ill, a corporation of Delaware No Drawing. FiledDec. 1960, Ser. No. 74,753 7 Claims. (Cl. 298-91) This invention relatesto a process for separating a hydrocarbon fraction such as a petroleumdistillate into two products, one of which consists of the straightchain paraifinic components of the fraction which is an excellent jetfuel and the other fraction of which is the cyclic and branched chainhydrocarbons which are thereafter converted into an eifective gasolineproduct of high octane number and desirable burning characteristics.More specifically, this invention concerns a process for recovering thenormal parafiinic components of a jet fuel hydrocarbon fraction havingan end boiling point not in excess of about 600 F. utilizing a molecularsieve 'sorbent as the separating agent to recover the normal paratfiniccomponents which are desirable jet fuel .ccnstitutents and thereafterreforming the raflinate stream from the separation stage of the processat mild reaction conditions to thereby produce a gasoline product havinga high octane number and desirable burning characteristics.

One object of this invention is to provide a process for recovering thenormal parafiinic components of a jet fuel boiling range fraction tothereby produce a product having optimum properties for use as a jetfuel. Another object of this invention is to provide a method forpretreating a gasoline boiling range fraction to remove the componentsof the fraction which are difficult to reform and thereby provide a feedstock to a reforming reaction which is capable of being reformed toproduce a high octane gasoline product at low-severity reactionconditions, at which conditions the yield and octane number of theresulting reformate are maximized. Still another object of thisinvention is to enhance the economic value of a gasoline boiling rangefraction by separating the fraction into component cuts, each havingoptimum properties for a particular use.

In one of its embodiments this invention relates to a combinationprocess which yields a fraction having optimum properties for jet fueluse and another fraction having optimum properties for use as a gasolinemotor fuel which comprises contacting a jet fuel boiling rangehydrocarbon fraction with a molecular sieve selective for normalhydrocarbons, separating a Iafiinate stream consisting of branched chainand cyclic hydrocarbons, recovering the normal hydrocarbons from themolecular sieve as said product having optimum properties for jet fueluse, reforming said raflinate stream in the presence of hydrogen and areforming catalyst at low-severity reforming conditions and recovering agasoline boiling range fraction from the reforming reaction product assaid fraction having optimum properties for gasoline motor fuel use.

One of the important characteristics required for petroleum fractionsboiling in the gasoline and lower kerosene boiling ranges for use asfuels in jet engines is that the fuel burns with a non-luminous flame.The achievement of this characteristic in a jet fuel permits a jetengine to operate at a higher combustion temperature for a giventemperature of the metal parts of the jet engine itself. That is, when afuel capable of burning with a non-luminous flame is utilized in a jetplane, the temperature differential between the combustion gas and themetallic components of the jet engine may be substantially greater andas a consequence, the fuel may be burned in a jet engine with a higherrate of efiiciency of fuel utilization and a greater thrust output fromthe engine can be ob- "ice tained at the permissible temperature limitof the metal components of the jet engine. Although most liquid,combustible hydrocarbons, can be employed as a source of fuel in jetengines, certain fractions of petroleum boiling in the gasoline rangeand lower kerosene boiling range are particularly suitable because oftheir high energy yield (thrust) per pound of fuel. Another desirablecharacter istic of a fuel for jet engine use is the absence ofluminosity when the fuel combustion products are exhausted from theexhaust port of the engine. Of the hydrocarbons which are liquid atground temperatures and pressure and which do not solidfy at the subzerotemperatures of the upper atmosphere in which jet engines customarilycruise on long range flights, the fractions boiling in the gasoline andlower kerosene boiling ranges, preferably up to about 500 F. and not inexcess of about 600 F. at normal pressures, are especially suitable forjet engine use. Of these normally liquid hydrocarbons it has been foundthat the most desirable species within this range of boiling points arethe normal paraflins. which, upon combustion, have the least degree ofluminosity and the highest thrust per pound of the various structuralclasses of hydrocarbons. On the other hand, the olefins, naphthenes,aromatics and branched chain hydrocarbons occurring within the foregoingboiling range materials burn with the highest degree of luminosity andyield the lowest thrust per pound of fuel. Accordingly, the higher thenormal paraflin' content of the hydrocarbon fractions utilizable as ajet fuel, generally within the range of carbon atom content of from C toabout C the more desirable is the fuel for jet engine use. Ideally,hydrocarbon fractions in the C to C range and composed of normalparaifinic hydrocarbons are the preferred fuels for jet engine use.

Branched chain and cyclic hydrocarbons, including particularly, aromatichydrocarbons, such as benzene and toluene, are, on the other hand,particularly suitable and especially preferred for gasoline fuels foruse in internal combustion engines. Thus, it is well-known that of thegasoline boiling range hydrocarbons the isoparaffins are much moredesirable for use in internal combustion engines than normalhydrocarbons, because of their more desirable antiknock ratings (knockresistance in internal combustion engines operated at high compressionratios) and the antiknock rating increases as the degree of branching ofthe aliphatic chain increases. Of the cyclic hydrocarbons boiling withinthe gasoline range, aromatic hydrocarbons have a substantially higheroctane number and more desirable burning characteristics in highcompression internal combustion engines than the correspondingnaphthenic hydrocarbons. Accordingly, for gasoline use in an internalcombustion engine, it is desirable to reform the hydrocarbon componentsboiling within the gasoline boiling range in order to increase theproportion of isoparaidnic hydrocarbons in the fraction and also todehydrogenate and isomerize the naphthenic components into aromatichydrocarbons, both of which classes have more desirable properties foruse in high compression internal combustion engines.

The process of this invention provides a means of segregating thecomponents present within a gasoline boiling range fraction ofhydrocarbons into (1) a fraction having optimum properties for jet fuelengine use and (2) a separate fraction, the components of which may bereformed into a product especially suitable for gasoline use in aninternal combustion engine. By segregating the normal parailiniccomponents from the gasoline boiling range feed stock in the presentpretreatment operation, a product is recovered from the pretreatmentstage consisting essentially of normal parafiins which are particularlysuitable and preferred for jet fuel engine use, leaving a rafinatestream or fraction which is particularly suitable and desirable as afeed stock to a reforming conversion from which a high quality gasolineproduct may be recovered having optimum properties for use in aninternal combustion engine operated at high compression ratios. Anadditional advantage of the pretreatment stage of the present process isthat by removing the normal paraffinic components from the feedstockprior to the reforming conversion, the latter stage of the process maybe operated at less severe reforming conditions to produce the sameoctane number of product than when the reforming conversion is attemptedon the same fraction prior to the removal of the normalparafiins. Theadvantages of operating at the less severe reforming reaction conditionsis particularly apparent in the substantially greater yield of thedesired product being obtained at the less severe reforming conditionsin that less of the product is converted to the undesired light gaseoushydrocarbons and coke. It is well-known that the reforming process is avigorous reaction which causes deep-seated changes in the structure ofthe hydrocarbons undergoing the reforming conversion. Hydrocracking,dearomatization, dehydrogenation and isomerization are thetypical'conversions' which take place during a typical reformingprocess. In general, the degree of dehydrogenation, isomerization andaromatization increases with an increase in the severity of the reactionconditions; that is, as the pressure and temperature conditions, thetime of contact of the feed stock with the catalyst are increased and assuch other factors as the amount of acidic component in the catalystcomposition are increased, the octane number of the product isincreased; but accompanying such increased conversion is a marked,simultaneous increase in the deposition of carbonaceous deposits on thecatalyst and the conversion of feed stock to-low molecular weight,normally gaseous hydrocarbons having little use when the desired endproduct is a normally liquid gasoline boiling range product.

The preferred source of the hydrocarbon fractions utilized as feedstocksin the present process are the gasoline and light gas oilfractions of straight-run petroleum dis tillates which containonly'small concentrations, if any, of olefinic hydrocarbons which, ifpresent, may interfere in the gasoline boiling range fraction utilizedas feed stock, the hydrocarbon fraction is contacted with a so-calledmolecular sieve type of solid sorbent containing pores into which thenormal parafiin components of the feed stock are selectively 'sorbed,but into which the branched chain and cyclic components present withinthe feed stock do not enter because the pore openings in the sorbent arenot of sufficient size to accommodate the branched chain and cyclichydrocarbon components having diameters greater than the pore openingsin the molecular sieve sorbent. The pores present in the structure ofsuch molecular sieve sorbents must have a crosssectional diameter ofabout 5 Angstrom units but not greater than about 6 Angstrom units inorder to exhibit the required selectivity to permit the entry of thenormal parafin isomers of the feed stock, while rejecting the branchedchain and cyclic hydrocarbons having crosssectional diameters greaterthan about 5 Angstrom units and are thus incapable of entering the poreopenings of the solid sorbent. The term sorbate, referred to herein isintended to designate those components of the hydrocarbon feed stockcapable of entering the pores of the sorbent and of being selectivelyretained thereby; the term rafinate is intended to refer to the branchedchain and cyclic components of the feed stock which have moleculardiameters greater than will permit their entry into the pores of thesorbent. It is the former sorbate component which constitutes'the selectfraction of the feedstock utilizable as the premium jet fuel producthereof and the raffinate fraction of the feed stock is the materialutilized herein as feed stock tothe subsequent reforming stage of theprocess from which a premium grad-e gasoline pro-duct is recovered.

the'processing steps involvedtin the present invention.

The most desired fractions are separated as straight-run petroleumdistillates boiling up to about 600 F. and more preferably, up to about500 F., the gasoline boiling range fraction of 400 F. end point beingseparated from the reformate product. Although straight-run distillatesconstitute one of the most desirable petroleum fractions for use in thepresent process as feed stockand for the production of a jet fuelproduct, fractions having similar boiling ranges may also be utilizedherein as charge stock, such as a fraction boiling up to 500 F.separated from the products of a catalytic cracking reaction (generallycontaining, however, higher concentrations of olefinic components thanthe corresponding boiling range fraction of a straight-rundistillate),gasoline boiling range stocks prepared by the polymerization of lowerolefinic hydrocarbons, such as propylene, butylene or mixed polymeriza:tion products of butylenes and propylene, gasoline boiling rangefractions of petroleum reformates (which, however, generally containhigher proportions. of aromatic components) and the generally.paraflinic products recovered from the Fischer-Tropsch synthesis, aswell; as a variety of other sources which provide gasoline boiling rangehydrocarbon fractions. Those charge stocks herein-v above specifiedwhich contain an appreciable proportion of olefinic'components arepreferably subjected to a prehydrogenation'treatment inthe presence ofa, suitable hydrogenation catalyst to convert these olefins to the cor-vresponding parafiins prior to the separation treatment provided herein.

In the separation step of the present process wherein the normalparaflinic components of the feed stock are selectivelyrecovered fromthe branched chain pa rafiiinic and cyclic components. which may also bepresent in Suitable molecular sieve sorbents of the type hereinabovedescribed, capable of sorbing and selectively retaining normal parafiinhydrocarbons within their porous structure include, particularly,certain metal aluminosilicates formed by the dehydration of thecorresponding zeolitic hydrated metal .alu min-ocilicates, which byvirtue of such dehydration containpores of about 5 Angstrom units incross-sectional diameter. Of these, the zeolitic calciumalumino-silicates, especially dehydrated to develop porous structures ofabout'S Angstrom units, constitute one of the most desirable andelfective sorbents contemplated herein, although other metalalumino-silicates in which the metal is selected from other alkalineearth metals such as barium, magnesium and cesium, or from such metalsas zinc, copper, iron, nickel, cobalt, etc., may also be prepared'andutilized as sorbents herein. The material known by its trade name asLinde 5A molecular sieves and 'Davison Chemical Company Microtraps aregenerally available commercial sources of sorbents for use in thepresent process. The sorbents are generally prepared by mixing asuitable source of silica sol or a silicic acid ester such as an alkalimetal silicate (sodium silicate or water-glass is a generally availablesource) or an alcohol'ester of silicic acid such as ethyl orthosilicatewith a source of an ionizable aluminum salt capable of yielding aluminaor aluminum hydroxide by reaction with the silicate or with alkali. Bymaintaining certain ratios of alkali metal to silica,

' alumina to silica and water to silica in the reaction mixture and byvmaintaining the temperature of the aqueous mixture at crystallizationconditions, a hydrated alkali metal alumino-silicate forms in a zeoliticcrystalline modification wshichmay thereafter be filtered, dried andcalcined at temperatures not in excess of about 500 C. to dehydrate thewater of crystallization from the alkali metal alumino-silicate, leavingpores within the resulting crystals having pore diameters of'about 4Angstrom units. The sorbents containing sieve pores of about 5 Angstromunits are prepared by ion-exchange of the alkali metal alumino-silicatewith an aqueous solution of a salt of the metal to be placed in thechemical composition of the ultimately desire-d molecular-sieve sorbent.Thus, in

order to form a calcuium alumino-silicate having pores of about 5Angstrom units, constituting one of the most desirable sorbents for usein the separation step of the present process, an aqueous slurry ofsodium aluminusilicate crystals in hydrated form is mixed with anaqueous solution of a calcuim salt, such as calcium chloride, which, byion-exchange, exchanges the sodium present in the alumino-silica-tecrystals with calcium. When the latter crystals, recovered from theresulting aqueous slurry, are dehydrated and calcined, molecular sievesorbent crystals having pore diameters of about 5 Aug strom units areproduced; these crystals are capable of being utilized directly in thesorption step of the present process or they may be oomposited with abinder clay, extruded into larger particles and thereafter utilized asthe present .sorbent.

Other selective sorbents of the molecular sieve type, capable ofselectively retaining the normal paraffin constituents of the presentfeed stock include, among others, certain activated carbons formed bycarbonization of acid-hydrocarbon sludges produced as by-products incertain acid-catalyzed hydrocarbon conversion processes, subsequentlycalcined at a temperature sufiicient to carbonize the sludgehydrocarbons, and thereafter washed with water to free the carbonizationresidue of any acidic material. Other sorbents of the molecular sievetype are prepared from certain activated aluminas formed by hightemperature calcination of aluminum oxide or aluminum hydroxide andcontaining pores having cross-sectional diameters of about 5 Angstromunits. Still another class of material utilizable herein as a molecularsieve sorbent for separating the normal paraffinic component from thefeed stock is urea in aqueous or alcoholic solution or, if utilized in afixed-bed type of process, the urea crystals themselves, which alsoselectively combine with the normal or straight chain components of thefeed stock to form molecular complexes or adducts capable of existing incrystalline form at certain temperatures, generally below about 40 C.After contact with the feed stock, the resulting adduct crystals areseparated, for example, by filtration, and the normal paraflincomponents separated from the crystals by heating the latter to atemperature above about 30 C. whereby the normal paraffin hydrocarbon-scomplexed with the urea separate out as an insoluble upper phase fromthe lower layer of molten urea crystals. In an alternative type ofseparation process, thiourea may be utilized as the adduct-forming'reagent, combining selectively with isoparafiinic and cyclichydrocarbons to form a crystalline adduct thereof. The normalparafiins-remain free and may be recovered from the adduct.

Processes for the utilization of molecular sieve sorbents and theprocess conditions required for their use are well-known in the priorart and reference is made herein to such art for the specific detailsinvolved in the use of such materials.

In carrying out the separation stage of the present combined process,the hydrocarbon feed stock is contacted with the molecular sieve sorbentat the particular temperature and pressure conditions and in eitherliquid or vapor state suitable for the particular molecular sievesorbent utilized in the separation stage. Thus, in the use of urea orthiourea as the separating agent, relatively low temperatures at whichthe feed stock exists in the liquid phase must be employed. Whenutilizing the refractory metal almino-silicate molecular sieves, on theother hand, either liquid or vapor phase operation may be utilized,although even in the use of the latter sorbents, relatively lowtemperatures and pressures sufficient to maintain the feed stock insubstantially liquid phase are preferred.

Upon contact with the particles of sorbent, the straight chaincomponents present in the feed stock selectively enter the pore openingsin the structure of the sorbent and are thereafter retained within thepores by physical 6 forces. the branched chain or cyclic hydrocarboncomponents of the feed stock continues its flow through the bed ofmolecular sieve sorbent and is ultimately withdrawn from the separationstep as the rafiinate fraction of the feed stock, hereinafter chargedinto the reforming stage of the process as feed stock thereto. Thenormal or straight chain components retained by the sorbent within theporous structure of the molecular sieve are recovered from the spentsorbent by desorption with a suitable displacing material or by a changeof the physical conditions which result in the displacement ordesorption of the retained normal paratfins from the molecular sievesorbent. A preferred method of desorption which enables the sorbent tobe utilized in a swing cycle process arrangement involves the use of onebed or" sorbent in the sorption stage to accept feed stock whilesimultaneously another bed of sorbent undergoes desorption whichregenerates the sorbent for further contact with the feed stock when thefluid streams entering the two beds of sorbent are subsequently shifted.This method of desorption depends upon the displacement of the sorbednormal component of the feed stock by surrounding the particle ofsorbent containing the sorbed normal component with a stream ofanother-normal hydrocar bon compound boiling above or below the boilingpoint of the sorbed normal component of the feed stock to enable themixture subsequently recovered to be readily separated by fractionaldistillation means. In this method of desorption, it is essential thatthe molar ratio of desorbent supplied to the sorbent particle issufiicient to cause the displacement by the mass action effect.

One of the preferred desorbents for use in the present process is anormal paraffin of lower molecular weight than the sorbed normalcomponent of the feed stock, although a paraffin of higher molecularweight may also be used as desorbent and in some instances may bepreferred. The desorbent is supplied to the spent sorbent in a quantitysuflicient to provide a mass action effect which displaces the sorbednormal parafiin from the molecular sieve sorbent and which may besubsequently fractionated from the desorption eflluent as an overhead,if a lower molecular weight paraffin is used as desorbent or as adistillation bottoms if a higher molecular weight paraflin is utilizedas desorbent. Thus, normal paraflins from normal butane to about normalhexane constitute suitable desorbents for use in the present processwhen the desorbent is to be fractionated from the desorption effluent asan overhead.

Desorption of the sorbed normal paraflin may also be effected by heatingthe spent sorbent and/ or reducing the. pressure thereon, preferablywhile passing through the spent sorbent a gas which is inert to both thesorbent and the sorbate component displaced from the spent sorbent.Thus, as a perfluent stream of an inert stripping gas such as nitrogen,isobutane, normal butane, carbon monoxide, methane, etc., is passedthrough the mass of spent sorbent, the mass of sorbent is heated byraising the temperature of the stripping gas and recovering the sorbatecomponent from the desorption effiuent by cooling and condensing thesorbate therefrom. Desorption is also promoted by reducing the ambientpressure on the spent sorbent While passing an inert gas through themass of sorbent. Stripping the sorbate component from the sorbent inthis manner thereby regenerates and reactivates the sorbent for repeatedreuse in the system.

The normal parafiin components recovered from the feed stock by themolecular sieve separation technique are especially desirable jet fuelsbecause of their high luminosity index rating and their desirableburning characteristics in that they produce a large thrust per pound offuel, being in this regard, much more effective for jet fuel purposesthan their corresponding branched chain and cyclic isomers.

The non-sorbed effluent, or rafiinate, comprising alumina-combinedhalogen type of reforming catalyst contains from about 0.01 percent toabout 1 percent by weight of a Group VIII noble metal, such as platinum,palladium or rhodium and from 0.1 percent to about percent by would berequired to obtain a product having the same octane number whenreforming the feed stock without removing the normal paraffins therefromin a preceding separation procedure.

.7 It is well-known that the degree of conversion or severity of thereforming conversion is influenced directly by several reactionvariables, including the temperature, the pressure, the space velocityof the feed stock relative to the catalyst, and the catalyst composition(mostly by the quantity of acidic component in the catalyst) and anyoneor more of these factors may be varied independently of the other toaffect the severity of the reaction. At the more severe reactionconditions, the proportion of feed stock converted to light,non-condensable gases such as hydrogen, methane, ethane andothernormally gaseous hydrocarbons is increased and inversely the amount ofliquid product constituting the desired end product of the processdecreases directly as the severity of thereaction conditions increases.It is also known that the octane number of the desired liquid productincreases in direct proportion to the severity of theprocess'conditions, caused by more deep-seated isomerization anddehydrogenation reactions occurring during the reforming conversion.However, it has now been found that when the normal paraffin componentsare removed from the charge stock prior to the reforming conversion, forexample, by the first stage of the process of this invention,'the sameor higher octane number may be obtained in the desired liquid portion ofthe product without increasing the severity of the reaction condition tothose'levels at which conversion of the normal components must beeffected.

. Although generally, conversion temperatures within the range of fromabout 800 to about 1000 F. or even higher are required to produce aproduct having an octane number in the range set for premium gasolines,generally above about 90 octane number, the present process may, on theother hand, be operated at, temperatures in the range of from about 650to about 850 F. whenutilizing the rafiinate feed stock provided herein.The pressure maintained within the reforming conversion reactor issuperatmospheric, up to about 3000 po unds per square inch, althoughthis reaction condition may be varied considerably without substantiallychanging the character of the product. Preferred pressures are fromabout 500 to about 1500 pounds per square inch gauge,'the depth ofconversion generally increasing as the pressuremaintained during theprocess is increased.

The reforming stage of the present process is preferably elfected in thepresence of a catalyst which is not only capable of effectingdehydrogenation of the naphthenes present in the feed stock to formaromatic hydrocarbons thereby, but is also capable of effectinghydrogenation and isomerization of the paraflinic and olefinichydrocarbons to form more highly branched chain com- 'ponents;

Satisfactory reforming catalysts for this purpose generally contain ametal oxide or sulfide of a metal selected from the elements of GroupVIII of the Periodic Table supported on a refractory oxide, such asalumina. One of the preferred catalysts for this purpose is platinumsupported on alumina containing an acidic. component combined with theplatinum and/ or alumina, the catalyst being described in US. Patent No.2,478,916, issued August 16, 1949. A particularly preferredcatalystcomposition useful in the reforming stage of the. process comprisesalumina composited with platinum and a combined halogen, of the typedescribed in US. Patent No. 2,479,- 109, issued August 16, 1949. Thepreferred platinum- Weight of a'combined halogen such as chlorine, or aportion of the chlorine may be replaced by fluorine in an amount of fromabout 0.1 percent to about3 percent by Weight of the total composite.The lower levels of halogen content are particularly suitable if theseverity of the reforming reaction is not reduced by reactiontemperature reduction. Other reforming type catalysts may also beeffectively utilized in the present process, including such catalystcompositions as molybdena-alumina composites containing from about 1percent up to about 20 percent by weight of molybdena, chromia-aluminacomposites containing from 1 percent up to about 25 percent by weight ofchromia, nickel and/ or cobalt oxide or sulfide composited with aluminaor combined with a preformed molybdena-alumina composite, as well asothers recognized in the petroleum refining art for their reformingcapacity.

V The reformingreaction is preferably effected in the presence ofhydrogen charged to the process in an amount sufficient to provide fromabout 1:1 to about 15:1 molar proportions of hydrogen per mol ofhydrocarbon feed stock,'the excess hydrogen usually being recycled inthe process until its'concentration in the recycle gas stream is reducedto less thanabout 50 mol percent. The reforming process is anequilibrium reaction, the formation of aromatic hydrocarbons bydehydrocyclization and isomerization being favored by high pressures upto about 3000 pounds per square inch gauge.

Depending upon whether the severity of the reforming reaction has beenreduced by a prior reduction in temperature and/or acidic component inthe catalyst composition, the rate of charging the feed stock relativeto the catalyst may also be increased in order to reduce the severity ofthe conversion. Thus, space velocities may be increased from about 0.5volume, of feed stock in the liquid state per volume of catalystper hourto liquid hourly space velocities in the range of from about 0.8 to 3.0,depending, as indicated, on the modification of other reaction variablesto reduce the severity.

The products of the reforming conversion comprising generallyanon-condensable gaseous fraction made up in large part of hydrogen maybe recycled to the reforming conversion until the mol percent ofhydrogen in the gas stream is reduced to less than about 50 mol percent.A normally liquid fraction containing C to about C hydrocarbons,generally a large proportion of which are of isoparaffinic and aromaticstructure is separated as a 'ples, which, however, are not introducedherein for the purpose of limiting the broad scope of the invention butmerely for illustrating working embodiments of the invention.

Example and cycloparaflinic) hydrocarbons containing from 4 to 12ca'rbon'atoms; Analysis of thefraction indicates that the hydrocarboncomponents are of the following types in the indicated proportions:

Percent by weight 11-Parafiins 38 Branched chain parafiins 46Cycloparafiins 12 Aromatics 4 The above fraction at a temperature of 30C. (i.e., in liquid phase) is permitted to flow downwardly through avertical column of the A molecular sieves until n-paraffins began toappear in the efiluent from the bottom of the column, as indicated byinfra-red analysis of timed samples of the effluent raffinate, theraffinate being separately reserved for subsequent conversion in thereforming stage of the present combination process. Approximately 1 ft.of molecular sieves for each 0.8 gallon of feed stock is required tocomplete the recovery of n-paraffins from the feed stock. The residualfeed stock remaining in the column is thereafter flushed from themolecular sieve particles with liquid isobutane charged at a pressure of20 lbs./in. the flush efiluent being separately recovered to determinethe volume of feed stock thereby recovered after distilling overhead theisobutane. The sorbed n-paraflins retained within the pores of thesieves are then recovered by passing a liquid stream of n-butane at 20lbs/in. through the column of spent sieves and collecting the desorbenteffiuent in a separate container. After distillation of the n-butanefrom the desorbent effluent, the residue is analyzed for n-paraflincontent, the analysis indicating that 98.6 percent of the sorbateproduct consists of n-paraflins of C C chain length and 95 percent ofthe n-paraflin content of the feed stock is recovered, the remainderconsisting of n-butane which is distilled overhead from the desorptioneffluent. When a suflicient quantity of the n-parafiin product had beenaccumulated to provide a test of these paraflins as fuel for a jetengine, the product was compared from the standpoint of luminosity,smoke production and thrust output with the initial feed stock mixture.These tests establish the superiority of n-parafiins as jet fuel, then-paraffin product burning with a clean, blue-white exhaust compared toa more highly luminous yellowish-red, smoky exhaust of the initial feedstock. The n-paraffin product yields a thrust output some 8 percentgreater than the initial feed stock mixture under similar testconditions.

The rafiinate effluent of the initial separation stage of the processutilizing the 5A molecular sieves and representing approximately 62percent by weight of the feed stock is composed for the most part ofcycloparafiins and slightly branched chain isoparaflins and has aResearch Method octane number (without added TEL) of 62.

The above raifinate efliuent is subjected to a reforming conversion bycharging the rafl'inate at a pressure of 700 lbs/in. and in the presenceof 1.5 mol percent hydrogen through a catalyst-packed tubular reactormaintained at a temperature of 700 F., the catalyst being a composite ofalumina with 0.375 percent by weight of platinum, 0.35 percent by weightof combined chlorine and 0.35 percent by weight of combined fluorine, inthe form of pellets fis-inch by /s-ir1ch size. The reformate product iscooled and the normally gaseous portion of the product at the processpressure is cooled to F. to separate a non-condensable gas fraction(consisting of 89 percent H and small quantities of methane and ethane)from the condensable gases consisting of C and C paraflins. The normallyliquid product (gasoline fraction) is distilled from the product to anend-point of 400 F. A yield of gasoline product of 96 weight percent isobtained, the product having a Research Method octane number (withoutadded TEL) of 96. Analysis of the gasoline product indicates that itcontains 24 percent by weight of aromatics formed by dehydrogenation andaromatization of the cycloparafiinic components and 69 percent by weightof isoparaffinic components of highly branched chain structure.

The overall yield of useful, liquid products is 96.5 percent by weightof the initial feed stock.

Example II In a second run utilizing the process flow of Example I,above, as well as the molecular sieve sorbent and the reforming catalystspecified in the foregoing example, except that the feed stock is afraction having an end boiling point of about 600 F. of a catalyticallycracked naphta, lightly prehydrogenated to eliminate olefinic com-Separation of the above fraction into an n-paraflin sorbate productutilizing 5A molecular sieves, in acocrdance with the proceduredescribed in Example I, yields a premium jet fuel containing 97.5percent n-paraflins in a yield representing 44 percent of the naphthacharged.

The rafiinate effluent of the foregoing separation, consisting of thebranched chain and cyclic paraffins, as well as the aromatics containedin the initial charge stock are subjected to reforming at the reactionconditions and with the catalyst specified in Example I, above. Theoctane number (Research Method, without added lead) of the charge stock(400 F. end point fraction) compared to the gasoline boiling range cutof the reformate product is 54 vs. 91.

In a similar reforming conversion in which the initial 600 F. end pointcharge stock is utilized as feed stock to the reforming reaction, butthe catalyst temperature is raised in 25 F. increments during thepassage of feed stock into the reaction zone until the reformate product(400 F. end point) has an octane number of 91, the catalyst temperaturemust be increased to 900 F. to obtain a gasoline boiling range productof the same octane number as the product obtained by conversion of theraffinate effiuent at 700 F. and the yield of gasoilne boiling rangeproduct is 84 percent by weight of the feed stock compared to 94 percentby weight of the feed stock based on utilizing the rafiinate efllucnt asfeed.

I claim as my invention:

1. A combination process for producing a fraction having optimumproperties for jet fuel use and another fraction having optimumproperties for use as a gasoline motor fuel which comprises contacting ahydrocarbon fraction predominating in saturated hydrocarbons of r from 4to 12 carbon atoms and having an end boiling point of from about 500 toabout 600 F. with a molecular sieve selective for normal paraffinichydrocarbons, separating a rafiinate stream consisting essentially ofbranched chain and cyclic hydrocarbons, recovering the normal paraflinichydrocarbons from the molecular sieve and removing the same, without anyfurther conversion thereof, from the process as said product havingoptimum properties for jet fuel use, reforming said raflinate stream inthe presence of hydrogen and a reforming catalyst at low-severityreforming conditions and recovering a gasoline boiling range fractionfrom the reforming reaction product as said fraction having optimumproperties for gasoline motor fuel use.

2. The process of claim 1 further characterized in that said hydrocarbonfraction is a straight-run petroleum distillate.

3. The process of claim 1 further characterized in that said hydrocarbonfraction has an end boiling point of about 500 F.

4. The process of claim 1 further characterized in that said molecularsieve is a dehydrated calcium aluminosilicate containing pores of about5 Angstrom units in cross-sectional diameter. r 5. The process of claim1 further characterized in that said reforming catalyst is'a compositeof alumina, platinum and a halogen selected from the group consisting ofchlorine and fluorine. 7 a 6. The process of claim 1 furthercharacterized in that said low-severity reformingconditions comprise areforming reaction temperature up to about 850 F.

7. The process of claim 1 further characterized in that 12 saidhydrocarbon fraction is a non-olefinic, catalytically crackedhydrocarbon fraction.

References Cited by the Examiner UNITED STATES PATENTS 2,479,110 8/49Haensel 208-139 2,952,614 7 9/60 Draeger eta]. 20891 3,012,961 12/61Weisz -0. 260667 3,081,255 3/63 Hess et al. 20888 ALPHONSO D. SULLIVAN,Primary Examiner.

1. A COMBINATION PROCESS FOR PRODUCING A FRACTION HAVING OPTIMUMPROPERTIES FOR JET FUEL USE AND ANOTHER FRACTION HAVINGOPTIMUMPROPERTIES FOR USE AS A GASOLINE MOTOR FUEL WHICH COMPRISESCONTACTING A HYDROCARBON FRACTION PREDOMINATING IN SATURATEDHYDROCARBONS OF FROM 4 TO 12 CARBON ATOMS AND HAVING AN END BOILINGPOINT OF FROM ABOUT 500*F. WITH A MOLECULAR SIEVE SELECTIVE FOR NORMALPARAFFINIC HYDROCARBONS, SEPARATING A RAFFINATE STREAM CONSISTINGESSENTIALLY OF BRANCHED CHAIN AND CYCLIC HYDROCARBONS, RECOVERING THENORMAL PARAFFINIC HYDROCARBONS FROM THE MOLECULAR SIEVE AND REMOVING THESAME, WITHOUT ANY FURTHER CONVERSION THEREOF, FROM THE PROCESS AS SAIDPRODUCT HAVING OPTIMUM PROPERTIES FOR JET FUEL USE, REFORMING SAIDRAFFINATE STREAM IN THE PRESENCE OF HYDROGEN AND A REFORMING CATALYST ATLOW-SEVERITY REFORMING CONDITIONS AND RECOVERING A GASOLINE BOILINGRANGE FRACTION FROM THE REFORMING REACTION PRODUCT AS SAID FRACTIONHAVING OPTIMUM PROPERTIES FOR GASOLINE MOTOR FUEL USE.